Many refrigerant systems for heating and/or cooling include a fixed orifice type of expansion device for metering refrigerant flow.
U.S. Pat. No. 5,581,883, for instance, shows a tubular flow restrictor with a fixed orifice opening. An outer tube is crimped to help hold the flow restrictor in position within the tube, and then the restrictor is soldered in place. Once installed with the outer tube, however, it appears that it would be quite difficult to ever replace the internal restrictor.
U.S. Pat. No. 4,869,290 discloses an expansion device that includes a threaded connection for installing or replacing an internal orifice piston; however the device is relatively complicated due to the piston being movable between a first position to engage a valve seat and a second position to engage a shoulder.
U.S. Pat. No. 3,077,903 discloses a flow control device, particularly useful in water lines. Rather than providing a fixed restriction, however, it appears that the device includes an internal element that deforms under pressure to help regulate the flow rate. Moreover, the device appears to be comprised of custom made parts, which can make such a device more expensive to produce in low quantities.
U.S. Pat. No. 1,490,123 and British Patent 795,208 disclose simple fluid-related devices; however, the devices do not appear suitable for use as a metering device for a refrigerant circuit. The '123 device is a valve bonnet, and the '208 device is a nozzle.
There appears to be a need for a simple, replaceable metering element that can be readily and affordably incorporated in refrigerant systems.